File management processes executed by operating systems and system applications typically do not implement secure file deletion. For example, in WINDOWS 95, deletion of a file does not make the contents of the file unrecoverable. In fact, it can be a relatively simple process to recover the deleted file. Further, many common software applications such as word processing, e-mail and spreadsheet applications write temporary files during operation. Although these applications typically automatically delete the temporary files, they do so using an insecure file deletion method leaving traces of the files on the hard drive or other storage device. Virtual memory files, such as swap files, also cause a problem in that file fragments are swapped in and out the virtual memory files during operation. The fact that information is thus available on a storage device despite having apparently been deleted generates a security risk that is unacceptable to many individuals and public and private organizations.
One method for alleviating this problem is simply to physically destroy the storage device such that any data stored thereon is unrecoverable. However, this is an understandably expensive and time consuming solution. As an alternative to physical destruction of the storage device, conventional secure file deletion products provide targeted secure file deletion functions. Examples of conventional products include NUKER (available from GENIO USA), MICROZAP (available from NEW TECHNOLOGIES INC.), BURNIT (available from SYNCRONYS SOFTCORP) and SECUREWIN (available from CIPHER LOGICS CORPORATION).
In general, "secure" deletion involves overwriting the appropriate space on the storage device with specified overwrite arrays to obscure the original data. The overwrite arrays can be random or pseudo-random data as well as defined character or data patterns. Further, a series of overwrites can be performed in sequence with different specified arrays to ensure that the data can not be recovered even by destructive analysis of the fixed storage media. Conventional targeted secure deletion products allow a user to select a file for deletion and then securely delete that file. Such products can also allow a user to secure delete all free media space on a storage device. Also, conventional secure delete products may allow a user to secure delete virtual memory files (e.g., swap files).
However, conventional secure file deletion products suffer from a number of problems. One problem is that the targeted nature of the conventional products relies upon user activation of the process. Further, the user only executes the secure deletion process at discrete points in time. Thus, during the period of time between successive executions, the storage device will contain insecurely deleted information. Further, conventional products can be prohibitively time consuming because, to secure a storage device, they have to process the entire device to overwrite all unused storage space.